The present invention relates to a wave guiding quantum electronic switch comprising
an electron-waveguide carrying substrate; PA1 electrodes located adjacent the electron waveguides and functioning to generate an electric field in the transverse direction of the electron waveguides; and PA1 electron reservoirs between which the electron waveguides extend;
wherein the electron waveguides have a transverse extension of the same order of magnitude as a wavelength for an electron-wave function in the electron waveguides.
The function of conventional electronic components, including microelectronic components, is based on the fact that charge transportation is effected by drift and diffusion of charge carriers. This restricts the speed of the components and when applying present-day techniques digital applications have an upper limit of about 5 Gbit/s, at least in the case of more complex functions, such as multiplexing. However, much higher bit rates than this can be achieved with individual components in optical transmission systems. For instance, a bit rate of 100 Gbit/s has been demonstrated for detectors and a bit rate of 40 Gbit/s for modulators. Extremely fast electronic components whose control requires very little energy input can be obtained, however, by utilizing the wave properties of the electrons. These high speed components have an extension of the same order of magnitude as the mean free path of the electrons, which when expressed in terms of wave functions corresponds to the coherence length of the electron wave function. In this case, charge transportation is effected essentially through ballistic transport of the electrons, in other words there is insufficient time for the electrons to be scattered through the component. The term "mesoscopic" has been devised for components of this size, in order to signify that the extension of the components in all directions is smaller than or comparable with the coherence length.
Several mesoscopic components are described in patents and in the technical literature. The Japanese Patent Application No. 63-93161 describes a component in the form of a quantum interferometric Mach-Zehnder interferometer constructed from gallium arsenide. The interferometer has two electron reservoirs between which two electron waveguides extend. Wave functions for electrons which travel in the electron waveguides are influenced by an electric or magnetic field in a manner to cause a phase shift between the wave functions. The wave functions can be caused to interfere with one another in this way and, for instance, to cancel each other out.
A similar mesoscopic interferometer is shown in European Patent Application No. EP 0 357 248. This interferometer, however, has a bandpass filter for the electron wave function, which restricts the electron velocity range and thereby enlargening the modulation depth of the interferometer.
A quantum interferometric transistor is illustrated in a conference contribution by Supriyo Datta: "Quantum Interference Transistors". The contribution is published in Extended Abstracts of the 20th International Conference on Solid State Devices and Materials, Tokyo, 1988, pp. 491-494. The transistor has similarities with a field-effect transistor, but is based on interference between electron wave functions in two parallel electron waveguides. The transistor is controlled with the aid of an electrode which generates an electric field in the electron waveguides and influences the electron wave functions.
A quantum interferometric directional coupler is illustrated in an article in Appl. Phys. Letters, 56(25), 18th June 1990, pp. 2527-2529, by N. Tsukada, et al, "Proposal of Novel Electron Wave Coupled Devices". This directional coupler has two electron waveguides, each of which has an input and an output and both of which are connected to a respective electron reservoir. The electron waveguides are connected in parallel in an interaction zone and interact with one another and the directional coupler is controlled with the aid of electrodes provided in the interaction zone.
The known components described above are based on interference between electron wave functions from separate electron waveguides or from coupling between electron wave functions in separate waveguides. In order to achieve good performance, it is necessary for the electron waveguides to be single-mode waveguides whose extension in the transverse direction of the waveguides is, for instance, from 50 to 100 .ANG., depending on the bandgap of the materials used. In the case of these components, good performance also demands a unitary electron velocity or, seen in another way, a unitary wavelength of the electron wave function, which is difficult to achieve. The components described above also have an output signal which varies periodically with the strength of an input signal, for instance as illustrated in FIG. 1b of the above-cited Supriyo Datta reference. This places demands on the accuracy of the control signal. Certain of the above-described components also have other drawbacks. One of these drawbacks is found in the manufacture of the quantum interferometric directional couplers, the physical length of which shall be equal to a coupling length. This places such high demands on manufacturing accuracy as to render the manufacture of the direction couplers almost impossible with present-day techniques.
The field of integrated optics also includes components which correspond to the above-described components, for instance optical directional couplers and Mach-Zehnder interferometers. An optical switch having a forked, branched light waveguide is known, a so-called optical digital switch whose function is based on single-mode propagation of a lightwave and not on the interference between separate propagation modes. The mesoscopic components differ from the optoelectrical components in several respects in an obvious way. Mesoscopic components are smaller than optoelectrical components by several orders of magnitude, for instance they have a length of 1 .mu.m as opposed to lengths of 100-1000 .mu.m. Correspondingly, the cross-sectional dimensions of the waveguides are 50 .ANG. and 1 .mu.m respectively. In the case of mesoscopic components, it is electrical currents, electrons, that are controlled and not light, photons, and the signals which control the mesoscopic components are smaller than the signals which control the optoelectrical components by several orders of magnitude. Expressed in the terms of quantum mechanics, one difference is that in the mesoscopic components fermions are controlled and not bosons, as in the case of optical components.